1. Field of the Invention
This invention generally relates to systems and methods for design-based inspection of wafers using repeating structures.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Inspection processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers to promote higher yield in the manufacturing process and thus higher profits. Inspection has always been an important part of fabricating semiconductor devices. However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful manufacture of acceptable semiconductor devices because smaller defects can cause the devices to fail.
Inspection processes can be limited by various noise sources on the wafer. For example, one common inspection method is the die-to-die method that involves comparing output of an inspection system generated for corresponding positions in different dies formed on the wafer. In this manner, output generated for similar structures in multiple dies can be compared and the results of the comparison can be used to detect defects in those structures. However, due to process variations across the wafer, corresponding positions in different dies may have different characteristics such as film thickness and color variation that, while not actually defects, can be misidentified as defects in the die-to-die methods. The variations between dies can be accommodated by increasing the thresholds that are used to detect defects. However, increasing the threshold will obviously eliminate the detection of the smallest defects on the wafers.
Some inspection methods and/or systems detect defects by comparing output generated for multiple locations within a single die. There are generally two types of methods that utilize this concept in current inspection systems. However, their applicability is limited. For example, for array areas such as SRAM or DRAM areas of a die, by knowing the cell size within the array, a cell-to-cell inspection can be performed on wafer inspectors. There are also some existing systems that analyze the image stream during inspection and look for repeating structures by performing auto-correlation analysis and looking for periodic patterns. However, both of these methods are limited to layouts that have some periodicity (e.g., in the x direction) with a certain period.
Accordingly, it would be advantageous to develop inspection systems and/or methods that do not have one or more of the disadvantages described above.